One particularly efficient and economical way to route electrical conductors is through the use of a ribbon cable, having a number of spaced parallel electrical conductors held in a thin, flexible layer of insulation, laid under carpeting in, for example, office areas. A change in direction in such a flat cable is achieved by sharply folding the cable upon itself so that stacked layers of the cable result at the bend. While such a method of changing direction can be employed with a ribbon cable having spaced copper wires which can undergo an immediate 90 or 180 degree bend, this method of changing direction is not suitable with a cable assembly including an optical fiber or a coaxial cable. Sharp bending of an optical fiber will result in light attenuation, while folding an optical fiber on itself will cause it to break. Folding of a coaxial cable will mechanically damage the shield, displace the dielectric between the conductor and shield, and cause a change in the impedance characteristics of the cable. Also, folding of a cable upon itself doubles its thickness, which could make the presence of the cable under carpeting more noticeable. Of course, bending of a flat cable in the plane of the cable results in no appreciable increase in cable thickness.
One recently-proposed generally flat coaxial cable assembly for use under carpeting includes a jacket of polyvinyl chloride (PVC) having a central portion, holding a small coaxial cable, and side portions each having a stress-bearing member of nylon. The stress-bearing members, which are relatively inelastic, are independently longitudinally movable in the jacket. Bending of the flat cable assembly in the plane of the flat cable causes the member at the inside of the bend to extend beyond the jacket while the member at the outside of the bend is drawn inside the jacket. As the stress-bearing members must move throughout the length of the cable assembly, the force required to form the bend is a function of the length of the cable assembly. For further information regarding the structure and operation of such a cable assembly, reference may be made to U.S. Pat. No. 4,419,538.
Another recently proposed generally flat fiber optic cable assembly is manufactured with a right angle turn section. The fiber optic filaments of the cable are held in tension and separated by combs. The filaments are embedded in a resin layer disposed between laminations. Bonding of the components is effected in a press under heat and pressure to form the required curved section in a flat fiber optic cable. For further information regarding the structure and manufacture of this cable assembly, reference may be made to U.S. Pat. No. 4,496,215.